Reaction of S{sub 2} and H{sub 2}S with Sn/Pt(111) surface alloys: Effects of metal{endash}metal bonding on reactivity towards sulfur
- Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973 (United States)
The surface chemistry of S{sub 2} and H{sub 2}S on polycrystalline Sn, Pt(111), and a ({radical}(3){times}{radical}(3))R30{degree}-Sn/Pt(111) surface alloy has been investigated using synchrotron-based high-resolution photoemission and {ital ab initio} self-consistent-field calculations. At 100{endash}300 K, S{sub 2} chemisorbs and reacts on polycrystalline tin to form metal sulfides. The reactivity of pure tin toward sulfur is large even at a temperature as low as 100 K. In contrast, tin atoms in contact with Pt(111) interact weakly with S{sub 2} or H{sub 2}S. Tin does not prevent the bonding of S to Pt in a ({radical}(3){times}{radical}(3))R30{degree}-Sn/Pt(111) surface alloy, but the alloy is less reactive toward H{sub 2}S than polycrystalline Sn or pure Pt(111). At room temperature, S{sub 2} and H{sub 2}S adsorb dissociatively on Pt sites of ({radical}(3){times}{radical}(3))R30{degree}-Sn/Pt(111). Upon the dosing of S{sub 2} and H{sub 2}S to ({radical}(3){times}{radical}(3))R30{degree}-Sn/Pt(111), one sees the formation of only a chemisorbed layer of sulfur (i.e., no sulfides of tin or platinum are formed). The Pt{endash}Sn bond is complex, involving a Sn(5s,5p){r_arrow}Pt(6s,6p) charge transfer and a Pt(5d){r_arrow}Pt(6s,6p) rehybridization that localize electrons in the region between the metal centers. These phenomena reduce the electron donor ability of Pt and Sn, and the metals are not able to respond in an effective way to the presence of species that are strong electron acceptors like S{sub 2}, HS, and S. The redistribution of charge produces surfaces that have a remarkable low reactivity toward sulfur. When compared to other admetals (Cu, Zn, Ag, Au), tin is the best choice as a site blocker that can enhance the tolerance of Pt reforming catalysts to sulfur poisoning. The Sn/Pt system illustrates how a redistribution of electrons that occurs in bimetallic bonding can be useful for the design of catalysts that are less sensitive to the presence of S-containing molecules.{copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 641512
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 10 Vol. 109; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
Similar Records
Temperature-programmed desorption investigation of the adsorption and reaction of butene isomers on Pt(111) and ordered Pt-Sn surface alloys
A new catalysis for benzene production from acetylene under UHV conditions: Sn/Pt(111) surface alloys